Six proposals are presented to explore pathogenic disease mechanisms in systemic lupus erythematosus, rheumatoid arthritis, vasculitic syndromes and steroid-induced osteopenia. In SLE, Dr. B. Hahn (rheumatology) will study subpopulations of anti-DNA antibodies in murine lupus and attempt to modify their disease by administration of anti-antibodies. Dr. B. Schwartz (genetics, rheumatology) will search for and characterize human lymphocyte surface antigens characteristic of active SLE. Dr. J. Atkinson (immunology, rheumatology) will study abnormalities of circulating phagocytic cells, with emphasis on cGMP and cAMP levels and in patients with SLE, rheumatoid arthritis and vasulitic syndromes. Osteopenia will be studied by Dr. T. Hahn (metabolism) who will investigate alterations of vitamin D metabolism in corticosteroid-treated rats. Dr. William Murphy (radiology) will develop a new computed tomography technique for accurate measurement of bone density to improve our ability to diagnose osteopenia and evaluate therapies. Mechanisms of hand tendon rupture in an animal model of rehumatoid arthritis will be studied by Dr. Paul Manske (orthopedics). He will determine the relative roles of synovitis, synovial fluid and vascular supply in tendon rupture in order to establish optimal surgical procedures.